Clean look, I like where you are storing the jack, and made use of the space where the jack was to keep a lower profile. Very nice job. Ive been considering doing something similar. Although your way take a little extra room, it is a much simpler approach to it then my idea.
May I suggest getting a mesh guard over your sub to protect it. I had mesh guards over my two 12” woofers in my pickup truck. They can handle a fair bit of weight put on top of them.